1. Field of the Invention
This invention relates to a method for the welding of non-ferrous metal sheets. More particularly, the invention concerns a method for the welding of thin sheets of nonferrous metal, such as aluminum, using commercially available welding equipment and procedures and resulting in reduced welding time and costs.                2. Description of Related Art        
While the welding of nonferrous metals, such as aluminum and aluminum alloys, has been commercially practiced for over sixty years, the welding of very thin nonferrous metal sheets is a difficult and demanding process, which requires highly specialized training and equipment, making such welding inefficient, expensive, and not commercially viable in most situations. The difficulty in welding very thin sheets of nonferrous metals, like aluminum, stems from their unique physical properties, which differ greatly from those of ferrous metals, such as steel. Thus, it is fitting that technologies for joining steel sheets have developed; whereas, the development of technologies for joining aluminum sheets has progressed much more slowly.
When attempting to weld aluminum sheets with a thickness of less than 0.050 inches several technical problems arise due to the properties of the metal. As soon as aluminum is exposed to open air, an oxide layer instantly forms on its surface. This layer protects the aluminum from corrosion and has very high melting point of approximately 3,600° F., several thousand degrees greater than the melting point of aluminum and aluminum alloys, which normally melt in the range of 1,100° F. to 1,250° F. Additionally, aluminum's high thermal conductivity causes heat to rapidly dissipate during welding, which makes it very difficult to obtain enough heat to join aluminum sheets. As one attempts to melt the oxide layer surrounding a thin aluminum sheet, the high temperature required coupled with the high conductivity of aluminum causes the thin underlying aluminum core to melt almost immediately resulting in splattering of liquid aluminum and effectively destroying the sheet at the location of the weld.
At the present time, only spot welding, spot seam welding, and projection welding can be used to weld very thin sheets of nonferrous metals, especially aluminum. Each method requires specialized and expensive equipment and the ability to apply high clamping forces to electrodes on both sides of the sheet or sheets. Each method also requires extensive and time consuming procedures for removal of the natural oxide layers that form on aluminum. Because of the significant expense involved, these methods have been commercially adopted only where product requirements do not permit substitution with more economical materials or processes.
The welding of thicker nonferrous metals, especially aluminum and aluminum alloys, can be accomplished by several recognized methods but the most commonly used are Tungsten Inert Gas (‘TIG’), also known as Gas Tungsten Arc Welding (‘GTAW’), and Metal Inert Gas (‘MIG’), which is also known as Gas Metal Arc Welding (‘GMAW’).
While TIG welding can be used on thinner aluminum than MIG, it is a much slower process and requires more highly trained and skilled operators as there are many variables that must be manually and simultaneously maintained to achieve satisfactory results. TIG welding is too slow for reasonable production applications and leads to increased labor costs as it requires higher levels of training of operators.
MIG welding is the preferred choice for most commercial applications due to the semi-automatic nature of the process which increases welding speed and dramatically reduces required skill levels and operator training. However, it is generally known to those of skill in the art that MIG welding of aluminum sheets requires sheets at least 0.080 inches thick. Even the latest Pulsed MIG equipment available today, which can reduce heat input into the weld, is limited to welding of sheets with a minimum thickness of at least 0.050 inches and with greatly reduced welding speeds.
The most commonly accepted method for welding thin nonferrous sheets is to increase the thickness of the sheeting until it is thick enough to allow “traditional” edge welding of the sheet edge to a heavier member or even to another sheet. In realistic terms, traditional MIG welding procedures would require nonferrous sheet thicknesses of at least 0.080 inches. TIG welding calls for a minimum thicknesses of 0.050 inches or perhaps even only 0.040 inches; however, TIG welding is a slower process and requires highly skilled welders to control the heat into the sheets to avoid “melt-back” and destruction of the sheet edges. With additional sheet thickness, slower welding speed, and expensive, skilled operators, conventional methods of welding thin nonferrous sheets result in considerable costs, which can be significantly reduced by the present invention.